The present application relates to a non-aqueous electrolyte battery which includes a non-aqueous electrolyte containing a non-aqueous solvent having a prescribed relative dielectric constant and which has largely improved battery characteristics.
A chargeable non-aqueous electrolyte secondary battery occupies an important position as a power source of portable electronic devices. In order to realize a reduction in size and weight of the electronic device, it has been demanded to devise to reduce the weight and size of a non-aqueous electrolyte secondary battery, thereby efficiently using a storage space within the electronic device. As such a non-aqueous electrolyte secondary battery, there are exemplified a lithium ion secondary battery and a polymer lithium battery each having high energy density and output density.
Such a non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode and a non-aqueous electrolyte. Concretely, a material capable of doping and dedoping a lithium ion is used for a positive electrode active material of the positive electrode and a negative electrode active material of the negative electrode. For example, lithium-transition metal oxides and the like are exemplified as the positive electrode active material, and specific examples thereof include LiCoO2, LiNiO2, LiNiXCo(1-x)O2 and LiMn2O4. Lithium and alloys thereof, carbon materials and the like are exemplified as the negative electrode active material, and graphite and the like are mainly used as the carbon material.
As to the non-aqueous electrolyte, in case of a lithium ion secondary battery, a non-aqueous electrolytic solution having a non-aqueous electrolyte salt dissolved in a non-aqueous solvent is used; and in case of a polymer lithium battery, a solid electrolyte obtained by gelatinizing a non-aqueous electrolytic solution with a polymer matrix is used. The non-aqueous solvent which is used for the non-aqueous electrolyte is prepared by mixing a high-boiling solvent having high dielectric constant and viscosity and a low-boiling solvent having low dielectric constant and viscosity.
Examples of the high-boiling solvent having high dielectric constant and viscosity include cyclic carbonic esters and lactones, for example, ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone. Since these solvents well dissolve an electrolyte salt therein, they are able to increase the number of lithium ions in the solvent. However, since the viscosity thereof is high, the mobility of a lithium ion becomes small.
Examples of the low-boiling solvent having low dielectric constant and viscosity include chain carbonic esters, for example, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate. These non-aqueous solvents hardly dissolve an electrolyte salt therein. However, since the viscosity thereof is low, the mobility of a lithium ion becomes high.
Accordingly, for the purposes of well dissolving an electrolyte salt and imparting an adequate viscosity, the non-aqueous electrolytic solution is prepared by mixing a high-boiling solvent having high dielectric constant and viscosity and a low-boiling solvent having low dielectric constant and viscosity as described above. However, in case of a polymer lithium battery, the choice of the non-aqueous electrolytic solution is restricted. In order to immerse the non-aqueous electrolytic solution in a polymer matrix, it is necessary to use a non-aqueous solvent having compatibility with the polymer matrix in the non-aqueous electrolytic solution. Also, in case of a polymer lithium battery, a soft aluminum laminated film is used as an exterior material. Therefore, in order to prevent swelling of the exterior material due to evaporation of the non-electrolytic solution from occurring, it is necessary to use a high-boiling non-aqueous solvent.